THISTLE FAMILY 243 



Inflorescence paniculate or corymbiform; leaves not triple-nerved. 

 Inflorescence elongate, not flat-topped. 



Heads numerous in a much branched panicle; involucre well imbricate. 

 Leaves distinctly toothed. 



Disk of the head about 1 cm. high and broad; leaves thickish. 



41. A. salicifoUus. 

 Disk 6-8 mm. high and broad; leaves thin. 42. A. paniculatus. 



Leaves entire, rarely denticulate, with more or less clasping bases. 

 Disk of the head nearly 1 cm. high and broad. 



Bracts linear-flUform, more or less squarrose. 43. A. hesperius. 

 Bracts linear, erect. 



Ligules purple. 44. A. fluviaiilis. 



Ligules white or sometimes pinkish. 



Bracts not with white midrib; leaves narrowly linear. 



45. A. Osterhoutii. 

 Bracts with white midrib; leaves lanceolate or oblong-lanceolate. 



46. A. laetivirens. 

 Disk of the head 6-8 mm. high and broad. 



Bracts linear, nearly of the same length; leaves narrowly linear. 



47. A. longulus. 

 Bracts oblong or linear-obloug, the outer shorter; leaves broadly Unear. 



48. A. roseolus. 

 Heads rather few, often soUtary on the leafy branches; bracts narrowly linear, 



nearly of the same length, the outer green. 49. A. Franklinianus. 



Inflorescence more or less flat-topped. 



Leaves lanceolate to linear-lanceolate, flrra; heads numerous. 



50. A. corymMformis. 

 Leaves narrowly linear, thin; heads few. 51. A. junciformis. 



XVIlr. LONCHOPHYLIil. 

 Stem softly pubescent; leaves lanceolate, not pale. 



Stem crisp-puberulent above; upper stem-leaves linear, sessile, but scarcely auricled. 



52. A. lonchophyllus. 

 Stem villous above; upper stem-leaves oblong-lanceolate, auriculate-clasping. 



53. A. eriocaulis. 

 Stem hispidulous above; leaves linear, pale green. 54. A. leucopsis. 



XIX. OCCIDENT.^LES. 



Bracts linear-subulate, acuminate, the inner almost caudate. 



Leaves linear-oblanceolate, acuminate, or the upper linear-lanceolate. 



55. A. subcaudatus. 

 Leaves linear. . 49. A. Franklinianus. 



Bracts linear, acute; lower leaves oblanceolate, the upper lanceolate, acute, usually 

 auriculate-clasping. 

 Disk about 1 cm. broad; stem-leaves linear or lance-linear; basal-leaves linear-ob- 

 lanceolate; bracts distinctly imbricate in 3-4 series. 56. A. occidentatis. 

 Disk 1.5 cm. or more wide; leaves lanceolate or oblanceolate, entire; bracts in about 

 2 series. 

 Bracts, at least the outer ones, wholly green; plant 2-4 dm. high. 



57. A. Fremontii. 

 Bracts with more or less distinct white margins below, green-tipped above. 

 Bracts with conspicuous rhombic-lanceolate green tips; dark green stem- 

 leaves oblanceolate, all except the uppermost. crenate and petioled; rays 

 dark blue. 58. vl. Umbachii. 



Bracts with less conspicuous lanceolate green tips; stem-leaves usually entire, 

 light green and glaucous; rays hght purple. 59. A. ciliomarginatus. 



XX. Adscendentes. 

 Heads few in a simple corymb. 



Heads less than 1 cm. high; upper leaves much reduced; stem 2-3 dm. high, slender. 



60. A. armeriaef alius. 

 Heads over 1 cm. high; leaves all ample; stems stout, 3-6 dm. high. 



81. A. diaboHcus. 

 Heads many In a leafy panicle. 



Heads about 1 cm. nigh; stem-leaves lanceolate or oblanceolate. 



Stems 2-3 dm. high; bracts usually more or less pubescent on the backs. 



Bracts with green midvein and tips, puberulent. 61. A. Underwoodii. 



Outer bracts wholly green, densely pubescent. 21. A. violaceus. 



Stems 4-6 dm. high; bracts glabrous on the backs; stem-leaves thick, oblanceolate; 

 panicle elongate. 62. A. Tweedyi. 



Heads less than 1 cm. high; stem-leaves linear or narrowly linear-oblanceolate. 

 Bracts not spinulose-tipped. 



Lower leaves oblanceolate; bracts glabrous, except the ciUate margins; plant 



, 1-3 dm. high. 63. A. adscendens. 



Lower leaves narrowly linear-oblanceolate. 



Bracts more or less hairy on the back. 64. A. Nelsonii. 



Bracts glabrous, except the ciUate margins. 



Leaves of the floral branches elongate, narrowly linear, ascending. 



65. A. NuUallii. 

 Leaves of the floral branches reduced, short, oblong, spreading. 



66. A. halophilus. 



